DESCRIPTION (investigator's abstract): The retinal pigment epithelium (RPE) is a monolayer of cells separating the neurosensory retina and the choroidal blood supply which performs a wide range of functions that are necessary to health of the retina. The transport of ions by these epithelial cells is critical to the visual process because it regulates the environment of the photoreceptors and because it helps maintain retinal adhesion. The long term objective of the work proposed here is to provide a detailed description of the mechanisms and regulation of this ion transport. Like other transporting epithelia, the RPE has an asymmetric distribution of ion pumps and conductances in its two membranes which make up cellular transport systems that mediate the transcellular movement of ions. Recently developed methods allow a detailed study of these conductances in single, isolated RPE cells. The immediate aims are: (1) to identify in single cells specific conductances that are thought to be the basis for transcellular ion transport; (2) to localize these conductances to the apical or the basolateral membrane; (3) to examine the regulation of specific conductances, especially with regard to modulation by cyclic AMP; and (4) to identify and characterize the single channels that are the molecular basis for the conductances. These aims will be pursued using the patch-clamp technique to record macroscopic and single-channel currents in intact RPE cells and in membrane fragments. It is expected that these studies will result in a better understanding of how individual transport molecules are regulated so as maintain normal transport function in the RPE.